Ankle syndesmosis disruptions are usually caused by severe external rotation ankle injuries. Surgery is recommended to reduce and internally fix the diastasis to prevent lateral talar shift, which could otherwise lead to post-traumatic arthrosis. Such surgical treatment usually involves tibio-fibular transfixation using a syndesmosis screw as recommended by the A.O. group (Arbeitsgemeinschaft für Osteosynthesefrage (Association for the Study of Internal Fixation)). Disadvantages of syndesmosis screw fixation include the need for a second operation for implant removal; implant fatigue and breakage; and loss of diastasis reduction following implant removal. Furthermore, prolonged non-weight bearing to avoid implant breakage prior to removal may cause further morbidity. In addition, studies have shown ligament healing to be inhibited by full immobilisation.
Movement of the distal fibula relative to the tibia is seen in normal ankle motion. Rigid fixation of the ankle syndesmosis, therefore, prevents normal physiological movement, until the rigid fixation device is removed, loosens or breaks.
Various methods of syndesmosis fixation have been studied before, including bioabsorbable implants (Thordarson D B, Hedman T P, Gross D, Magre G. “Biomechanical evaluation of polylactide absorbable screws used for syndesmosis injury repair” Foot Ankle Int 1997; 18: 622-7) and flexible implants (Miller R S, Weinhold P S, Dahners L E. “Comparison of tricortical screw fixation versus a modified suture construct for fixation of ankle syndesmosis injury: a biomechanical study” J Orthop Trauma 1999; 13: 39-42; Seitz W H Jr, Bachner E J, Abram L J, Postak P, Polando G, Brooks D B, Greenwald A S. “Repair of the tibiofibular syndesmosis with a flexible implant” J Orthop Trauma 1991; 5: 78-82). Seitz used a suture-button fixation using a large polyethylene button, as is commonly used for tendon repair pull-out sutures and a No. 5 braided polyester suture. Seitz's operative technique involved opening both the medial and lateral sides of the ankle. On biomechanical testing, failure occurred through the polyethylene button at an average of 20 kg of tension, and through the suture at 28 kg. Clinical testing in 12 patients showed good results, one patient having a symptomatic medial button. Buttons were routinely removed at 8 to 12 months, and were all found to be intact. Miller compared a modified suture construct against tricortical screw fixation at 2 cm and 5 cm above the ankle mortise. This method also required opening both the medial and lateral sides of the ankle. No. 5 braided polyester suture was looped through two holes drilled across the distal tibia and fibula. Similar results were seen for the suture and screw fixations, with a better holding strength for both groups at 5 cm.
It is an object of the present invention to overcome the problems associated with the prior art, whilst permitting normal physiological movement of the fibula relative to the tibia.